The present invention relates to control systems for controlling the operation of a personal transport vehicle, such as a wheelchair, while climbing or descending stairs.
A major challenge for wheelchair designers has been to design a wheelchair which can safely and effectively ascend and descend stairs, and yet not be unduly large, cumbersome or expensive. One design is shown in U.S. Pat. No. 4,674,584. The wheelchair travels on normal wheels during horizontal operation, and has ultrasonic sensors detecting the presence of a stairway or other incline. The sensor signals are used to activate and lower a pair of tracks, which are looped endless treads. In addition to lowering the tracks, a signal from the ultrasonic sensors is also used to determine if the incline is too steep for the wheelchair to negotiate. In such an instance, the wheelchair will not be allowed to move forward and up or down the stairs.
One problem with movement down a stairway is that as a wheelchair edges over the stairway, it will suddenly tilt downward and slam onto the stairway, jolting the user or potentially injuring the user. A solution to this problem is described in U.S. Pat. No. 4,671,369. Forward and rearward arms are deployed beneath the wheelchair and extend downward over the stairs as the wheelchair approaches. As the body of the wheelchair begins to tilt down the stairs, the arm is already resting across the steps. A shock absorbing, fluid-filled cylinder between this extended arm and the body of the wheelchair ensures that the body of the wheelchair will slowly ease into position pointing down the stairway. The shock absorber is simply a tube with a piston extending through it and fluid therein to slow the movement of the piston through the cylinder. The '369 patent shows a mechanical linkage mechanism for deploying these cushioning arms.
In order to provide maximum comfort for a user during the ascending or descending of stairs, the seat is tilted so that the user is held horizontal while the body of the wheelchair is inclined. This tilting movement is also necessary to move the center of gravity of the wheelchair and the user to an appropriate position to allow it to safely climb the stairs. If the center of gravity is too far forward, away from the stairs, the wheelchair might roll. Thus, there is a danger, that without this tilting mechanism, and its attendant control of the center of gravity, the wheelchair could roll.
Motorized wheelchairs come in many different types, depending upon the abilities of the person expected to use the wheelchair. Some wheelchairs have stair climbing capabilities and other characteristics. A joystick is used as a typical input mechanism to control both the speed and direction of the wheelchair. However, some wheelchair users are unable to operate a joystick because of their disability. Other input mechanisms include voice control, head gear responsive to movements of the head, and an air pressure sensor responsive to blowing and sucking through a straw. Depending upon the type of input used, the input circuitry must be modified to handle input signals and provide the appropriate drive signals to the wheelchair motors in response.
In addition, even for a specific type of input, such as a joystick, there are variations among users. For instance, some users can operate s joystick only marginally since their hand may be constantly shaking. Thus, special filtering circuitry can be included to cancel out the effects of such shaking. In addition, a user may be able to only provide jerky movements, which would result in very rapid acceleration or deceleration unless modified. These modifications can be done by using different circuitry or providing switches as inputs to a processor in the back of the wheelchair which can be configured in accordance with a particular user's needs. Obviously, the use of such switches makes the circuitry complicated and requires a technician to configure the wheelchair for the particular user, adding to the costs. U.S. Pat. No. 4,634,941, for example, discloses in Col. 8 the use of variable resistances to control acceleration and deceleration.
Some wheelchairs are used in a multiple-user environment, such as a convalescent home, where the wheelchair must be reconfigured each time a new user is provided with the wheelchair. In addition, access to the wheelchair must be controlled where there is danger that a particular user may be injured in a wheelchair not adapted to that user's particular disabilities.